Crash an reboot problems...

I'm having some problems with system crashed and while I'm looking into
the background of those, I have to live with them. Only a crash that is
reproducable can be traced.

The last one was pretty bad, because it pretty much screwed up one file
system. The file system in question is completely unimportanted and
because of this fact it was mounted async (to increase write performance).

The problem is that now NetBSD won't start up anymore. What I get is
[1]. It is my understanding that NetBSD should normally drop down to
single user mode, where I could run fsck manually or it I have to do a
newfs on the partition in question. Is there any way I can get that done?